A communications apparatus including a wireless base station and a wireless terminal may be configured to implement a wireless communication function. For a communications apparatus, during signal reception, the communications apparatus receives, by using an antenna, a radio frequency (RF) signal sent by a wireless communications peer end, converts the RF signal to an analog baseband signal, and further converts the analog baseband signal to a digital baseband signal by using an analog-to-digital converter (ADC). The communications apparatus may further perform demodulation processing on the digital baseband signal according to a wireless communications protocol, for example, a series of operations such as channel estimation, channel decoding, and signal demodulation. During signal transmission, the communications apparatus performs modulation processing on a digital baseband signal according to a wireless communications protocol, for example, a series of operations such as signal modulation, channel encoding, and signal flow interleaving, converts an obtained processing result of the digital baseband signal to an analog baseband signal, further converts the analog baseband signal to an RF signal, and sends the RF signal by using an antenna.
In actual application, during signal reception, the communications apparatus mainly includes an RF part that converts an RF signal to an analog baseband signal and a baseband processor that performs modulation/demodulation processing on the analog baseband signal. The baseband processor may include the analog-to-digital converter and a digital baseband communications processor. The digital baseband communications processor runs wireless communications protocol software to perform demodulation processing on the digital baseband signal output by the analog-to-digital converter. The wireless communications protocol software may comply with or support at least one RAT (radio access technology) of LTE (Long Term Evolution), CDMA2000 (Code Division Multiple Access 2000), WCDMA (Wideband Code Division Multiple Access), TD-SCDMA (Time Division-Synchronous Code Division Multiple Access), or GSM (Global System for Mobile Communications). One RAT is a wireless communications protocol or a communication system.
During signal reception, the RF part may transmit the converted-to analog baseband signal to the baseband processor in a manner of a single-ended signal or a differential signal. FIG. 1 shows a typical differential signal transmission manner. An RF part performs down-conversion on a received signal, to convert the signal to two differential analog baseband signals RX+ and RX−, and transmit the two differential analog baseband signals RX+ and RX− to a baseband processor. During signal transmission, the baseband processor sends two differential analog baseband signals TX+ and TX− to the RF part, and the RF part performs up-conversion on the two differential analog baseband signals TX+ and TX− to convert the two differential analog baseband signals TX+ and TX− to a to-be-sent RF signal, and sends the RF signal by using an antenna.
In the differential signal transmission manner, two analog interfaces need to be disposed on the RF part and the baseband processor separately. This increases complexity and costs of hardware for interface implementation. Therefore, using a single-ended signal transmission manner between the RF part and the baseband processor is more conducive to cost reduction. FIG. 2 shows a typical single-ended signal transmission manner. There is only one received signal RX and one sent signal TX between an RF part and a baseband processor. Relative to FIG. 1, a quantity of interfaces used on both the RF part and the baseband processor in FIG. 2 changes from 4 to 2.
However, in the single-ended signal transmission manner, a direct-current component of an analog baseband signal RX transmitted by the RF part to the baseband processor, that is, a large-signal voltage, a bias voltage, or a common-mode voltage, is very likely to exceed a dynamic input range of an analog circuit in the baseband processor, for example, the analog-to-digital converter. This raises a quite high requirement for a large dynamic input range of the analog-to-digital converter, and it is highly complicated to implement the analog-to-digital converter having the large dynamic input range. Therefore, this also increases design and manufacturing costs.